Gratings Of Spatial Frequency Research Articles

Retinal inputs that drive optomotor responses of mice under mesopic conditions

Optomotor responses are a popular way to assess sub-cortical visual responses in mice. We studied photoreceptor inputs into optomotor circuits using genetically-modified mice lacking the exocytotic calcium sensors synaptotagmin 1 (Syt1) and 7 (Syt7) in rods or cones. We also tested mice that in which cone transducin, GNAT2, had been eliminated. We studied spatial frequency sensitivity under mesopic conditions by varying the spatial frequency of a grating rotating at 12deg/s and contrast sensitivity by varying luminance contrast of 0.2 c/deg gratings. We found that eliminating Syt1 from rods reduced responses to a low spatial frequency grating (0.05 c/deg) consistent with low resolution in this pathway. Conversely, eliminating the ability of cones to respond to light (by eliminating GNAT2) or transmit light responses (by selectively eliminating Syt1) showed weaker responses to a high spatial frequency grating (3 c/deg). Eliminating Syt7 from the entire optomotor pathway in a global knockout had no significant effect on optomotor responses. We isolated the secondary rod pathway involving transmission of rod responses to cones via gap junctions by simultaneously eliminating Syt1 from rods and GNAT2 from cones. We found that the secondary rod pathway is sufficient to drive robust optomotor responses under mesopic conditions. Finally, eliminating Syt1 from both rods and cones almost completely abolished optomotor responses, but we detected weak responses to large, bright rotating gratings that are likely driven by input from intrinsically photosensitive retinal ganglion cells.

Contrast sensitivity, visual acuity, and the effect of behavioural state on optokinetic gain in fiddler crabs.

Most animals rely on visual information for a variety of everyday tasks. The information available to a visual system depends in part on its spatial resolving power and contrast sensitivity. Due to their competing demands for physical space within an eye, these traits cannot simultaneously be improved without increasing overall eye size. The contrast sensitivity function is an integrated measure of visual performance that measures both resolution and contrast sensitivity. Its measurements helps us identify how different species have made a trade-off between contrast sensitivity and spatial resolution. It further allows us to identify the evolutionary drivers of sensory processing and visually mediated behaviour. Here, we measured the contrast sensitivity function of the fiddler crab Gelasimus dampieri using their optokinetic responses to wide-field, moving, sinusoidal intensity gratings of different orientations, spatial frequencies, contrasts, and speeds. We further tested whether the behavioural state of the crabs (i.e. whether crabs are actively walking or not) affects their optokinetic gain and contrast sensitivity. Our results from a group of five crabs suggest a minimum perceived contrast of 6%, and a horizontal and vertical visual acuity of 0.4 cyc/deg and 0.28 cyc/deg respectively in the crabs' region of maximum optomotor sensitivity. Optokinetic gain increased in moving crabs compared to restrained crabs, adding another example of the importance of naturalistic approaches when studying the performance of animals.

Association between retinal and cortical visual electrophysiological impairments in schizophrenia.

Electrophysiological impairments in the magnocellular visual system have been reported among patients with schizophrenia, but previous theories proposed that these deficits may begin in the retina. We therefore sought to evaluate the potential contribution of the retina by comparing retinal and cortical visual electrophysiological impairments between patients with schizophrenia and healthy controls. We recruited patients with schizophrenia and age- and sex-matched healthy controls. We recorded the P100 amplitude and latency using electroencephalography (EEG) while projecting low (0.5 cycles/degree) or high (15 cycles/degree) spatial frequency gratings at a temporal frequency of 0 Hz or 8 Hz. We compared the P100 results with previous results for retinal ganglion cell activity (N95) in these participants. We analyzed data using repeated-measures analysis of variance and correlation analyses. We recruited 21 patients with schizophrenia and 29 age- and sex-matched healthy controls. Results showed decreased P100 amplitude and increased P100 latency among patients with schizophrenia compared with healthy controls (p < 0.05). Analyses reported the main effects of spatial and temporal frequency but no interaction effects of spatial or temporal frequency by group. Moreover, correlation analysis indicated a positive association between P100 latency and previous retinal results for N95 latency in the schizophrenia group (p < 0.05). Alterations in the P100 wave among patients with schizophrenia are consistent with the deficits in early visual cortical processing shown in the literature. These deficits do not seem to correspond to an isolated magnocellular deficit but appear to be associated with previous retinal measurements. Such an association emphasizes the role of the retina in the occurrence of visual cortical abnormalities in schizophrenia. Studies with coupled electroretinography-EEG measurements are now required to further explore these findings. https://clinicaltrials.gov/ct2/show/NCT02864680.

A deep neural network model of the primate superior colliculus for emotion recognition.

Although sensory processing is pivotal to nearly every theory of emotion, the evaluation of the visual input as ‘emotional’ (e.g. a smile as signalling happiness) has been traditionally assumed to take place in supramodal ‘limbic’ brain regions. Accordingly, subcortical structures of ancient evolutionary origin that receive direct input from the retina, such as the superior colliculus (SC), are traditionally conceptualized as passive relay centres. However, mounting evidence suggests that the SC is endowed with the necessary infrastructure and computational capabilities for the innate recognition and initial categorization of emotionally salient features from retinal information. Here, we built a neurobiologically inspired convolutional deep neural network (DNN) model that approximates physiological, anatomical and connectional properties of the retino-collicular circuit. This enabled us to characterize and isolate the initial computations and discriminations that the DNN model of the SC can perform on facial expressions, based uniquely on the information it directly receives from the virtual retina. Trained to discriminate facial expressions of basic emotions, our model matches human error patterns and above chance, yet suboptimal, classification accuracy analogous to that reported in patients with V1 damage, who rely on retino-collicular pathways for non-conscious vision of emotional attributes. When presented with gratings of different spatial frequencies and orientations never ‘seen’ before, the SC model exhibits spontaneous tuning to low spatial frequencies and reduced orientation discrimination, as can be expected from the prevalence of the magnocellular (M) over parvocellular (P) projections. Likewise, face manipulation that biases processing towards the M or P pathway affects expression recognition in the SC model accordingly, an effect that dovetails with variations of activity in the human SC purposely measured with ultra-high field functional magnetic resonance imaging. Lastly, the DNN generates saliency maps and extracts visual features, demonstrating that certain face parts, like the mouth or the eyes, provide higher discriminative information than other parts as a function of emotional expressions like happiness and sadness. The present findings support the contention that the SC possesses the necessary infrastructure to analyse the visual features that define facial emotional stimuli also without additional processing stages in the visual cortex or in ‘limbic’ areas.This article is part of the theme issue ‘Cracking the laugh code: laughter through the lens of biology, psychology and neuroscience’.

Scalp-recorded N40 visual evoked potential: Sensory and attentional properties.

N40 is a well‐known component of evoked potentials with respect to the auditory and somatosensory modality but not much recognized with regard to the visual modality. To be detected with event‐related potentials (ERPs), it requires an optimal signal‐to‐noise ratio. To investigate the nature of visual N40, we recorded EEG/ERP signals from 20 participants. Each of them was presented with 1800 spatial frequency gratings of 0.75, 1.5, 3 and 6 c/deg. Data were collected from 128 sites while participants were engaged in both passive viewing and attention conditions. N40 (30–55 ms) was modulated by alertness and selective attention; in fact, it was larger to targets than irrelevant and passively viewed spatial frequency gratings. Its strongest intracranial sources were the bilateral thalamic nuclei of pulvinar, according to swLORETA. The active network included precuneus, insula and inferior parietal lobule. An N80 component (60–90 ms) was also identified, which was larger to targets than irrelevant/passive stimuli and more negative to high than low spatial frequencies. In contrast, N40 was not sensitive to spatial frequency per se, nor did it show a polarity inversion as a function of spatial frequency. Attention, alertness and spatial frequency effects were also found for the later components P1, N2 and P300. The attentional effects increased in magnitude over time. The data showed that ERPs can pick up the earliest synchronized activity, deriving in part from thalamic nuclei, before the visual information has actually reached the occipital cortex.

Contrast sensitivity is formed by visual experience and task demands

The contrast sensitivity function (CSF) is a fundamental signature of the visual system and has been measured extensively in numerous species. It is defined by measurements of the visibility threshold for sinusoidal gratings at all spatial frequencies. Here, we measured the CSF in artificial visual systems, namely deep neural networks (DNNs), using the same contrast discrimination paradigm as used in human psychophysical experiments. During training, networks are exclusively exposed to natural images, and the task is to identify which one of two input images has higher contrast. The contrast discriminator networks learn a linear classifier over frozen features of pretrained DNNs. At the testing stage, we measured the network's CSF by presenting sinusoidal gratings of different orientations and spatial frequencies. Our results demonstrate that the pretrained DNNs show the band-limited, inverted U-shaped CSF, that is characteristic of the human CSF. The exact shape of the DNNs' CSF appears to be task-dependent. The human CSF is better captured by scene segmentation DNNs than image classification ones (tested under identical settings such as the architecture and computational complexity). When the network was trained to discriminate the contrast in natural images from scratch (i.e., with no previous training task), a relatively flat CSF emerged, dissimilar to the human CSF. The environment of pretrained DNNs proved influential as well. Those with a diet of natural images, similar to human experience (e.g. objects or faces), obtain more human-like CSF. Pretrained DNNs with aerial pictures, such as a bird flying in the sky would see, obtain a shifted CSF towards higher spatial frequencies, similar to that of an eagle. In conclusion, the CSFs derived from the DNNs are the result of efficient processing of the natural world around us. Different visual environments have succinct effects on the shape of the CSFs.

Impaired P100 among regular cannabis users in response to magnocellular biased visual stimuli

Regular cannabis using causes vision impairment by affecting human retinal neurotransmission. However, studies less considered its impact on the subsequent visual cortical processing, key feature for the integration of the visual signal in brain. We aimed at investigating this purpose in regular cannabis users using spatial frequencies and temporal frequencies filtered visual stimuli.We recruited 45 regular cannabis users and 25 age-matched controls. We recorded visual evoked potentials during the projection of low spatial frequency (0.5 cycles/degree) or high spatial frequency gratings (15 cycles/degree), which were presented statically (0 Hz) or dynamically (8 Hz). We analyzed the amplitude, latency, and area under the curve of both P100 and N170, best EEG markers for early visual processing. Data were compared between groups by repeated measures ANCOVA.Results showed a significant decrease in P100 amplitude among regular cannabis users in low spatial frequency (F(1,67) = 4.43; p = 0.04) and in dynamic condition (F(1,67) = 4.35; p = 0.04). Analysis also reported a decrease in P100 area under the curve in regular cannabis users to low spatial frequency (F(1,67) = 4.31; p = 0.04) and in dynamic condition (F(1,67) = 7.65; p < 0.01). No effect was found on P100 latency, N170 amplitude, latency, or area under the curve.We found alteration of P100 responses to low spatial frequency and dynamic stimuli in regular cannabis users. This result could be interpreted as a preferential magnocellular impairment where such deficit could be linked to glutamatergic dysfunction. As mentioned in the literature, visual and electrophysiological anomalies in schizophrenia are related to a magnocellular dysfunction. Further studies are needed to clarify electrophysiological deficits in both populations. Clinical trials registrationElectrophysiological Study of the Functioning of Magnocellular Visual Pathway in Regular Cannabis Users (CAUSA MAP). [NCT 02864680; ID 2013-A00097–38]. https://clinicaltrials.gov/ct2/show/NCT02864680?cond=Cannabis&cntry=FR&draw=2&rank=1

Aligning one’s sights: The pulvinar provides context for visual information processing

The pulvinar (lateral posterior [LP]), like other higher-order thalamic nuclei, receives input from-and sends output to-multiple neocortical structures. In this issue of Neuron, Blot etal. (2021) demonstrate that LP integrates multimodal inputs to put visual information in context.

Spatial and temporal resolution of optogenetically recovered vision in ChR2-transduced mouse retina

Objective. Retinal ganglion cells (RGCs) represent an attractive target in vision restoration strategies, because they undergo little degeneration compared to other retinal neurons. Here we investigated the temporal and spatial resolution in adult photoreceptor-degenerated (rd10) mouse retinas, where RGCs have been transduced with the optogenetic actuator channelrhodopsin-2 (ChR2). Approach. The RGC spiking activity was recorded continuously with a CMOS-based microelectrode array during a variety of photostimulation protocols. The temporal resolution was assessed through Gaussian white noise stimuli and evaluated using a linear-nonlinear-Poisson model. Spatial sensitivity was assessed upon photostimulation with single rectangular pulses stepped across the retina and upon stimulation with alternating gratings of different spatial frequencies. Spatial sensitivity was estimated using logistic regression or by evaluating the spiking activity of independent RGCs. Main results. The temporal resolution after photostimulation displayed an about ten times faster kinetics as compared to physiological filters in wild-type RGCs. The optimal spatial resolution estimated using the logistic regression model was 10 µm and 87 µm based on the population response. These values correspond to an equivalent acuity of 1.7 or 0.2 cycles per degree, which is better than expected from the size of RGCs’ optogenetic receptive fields. Significance. The high temporal and spatial resolution obtained by photostimulation of optogenetically transduced RGCs indicate that high acuity vision restoration may be obtained by photostimulation of appropriately modified RGCs in photoreceptor-degenerated retinas.

Classification images for contrast discrimination

Contrast discrimination measures the smallest difference in contrast (the threshold) needed to successfully tell two stimuli apart. The contrast discrimination threshold typically increases with contrast. However, for low spatial frequency gratings the contrast threshold first increases, but then starts to decrease at contrasts above about 50%. This behaviour was originally observed in contrast discrimination experiments using dark spots as stimuli, suggesting that the contrast discrimination threshold for low spatial frequency gratings may be dominated by responses to the dark parts of the sinusoid. This study measures classification images for contrast discrimination experiments using a 1 cycle per degree sinusoidal grating at contrasts of 0, 25%, 50% and 75%. The classification images obtained clearly show that observers emphasize the darker parts of the sinusoidal grating (i.e. the troughs), and this emphasis increases with contrast. At 75% contrast, observers almost completely ignored the bright parts (peaks) of the sinusoid, and for some observers the emphasis on the troughs is already evident at contrasts as low as 25%. Analysis using a Hammerstein model suggests that the bias towards the dark parts of the stimulus is due to an early nonlinearity, perhaps similar to that proposed by Whittle.

Hemispheric Asymmetry in Visual Processing: An ERP Study on Spatial Frequency Gratings

A hemispheric asymmetry for the processing of global versus local visual information is known. In this study, we investigated the existence of a hemispheric asymmetry for the visual processing of low versus high spatial frequency gratings. The event-related potentials were recorded in a group of healthy right-handed volunteers from 30 scalp sites. Six types of stimuli (1.5, 3 and 6 c/deg gratings) were randomly flashed 180 times in the left and right upper hemifields. The stimulus duration was 80 ms, and the interstimulus interval (ISI) ranged between 850 and 1000 ms. Participants paid attention and responded to targets based on their spatial frequency and location. The C1 and P1 visual responses, as well as a later selection negativity and a P300 component of event-related potentials (ERPs), were quantified and subjected to repeated-measure analyses of variance (ANOVAs). Overall, the performance was faster for the right visual field (RVF), thus suggesting a left hemispheric advantage for the attentional selection of local elements. Similarly, the analysis of the mean area amplitude of the C1 (60–110 ms) sensory response showed a stronger attentional effect (F+L+ vs. F−L+) at the left occipital areas, thus suggesting the sensory nature of this hemispheric asymmetry.

Differential roles of pyramidal and fast-spiking, GABAergic neurons in the control of glioma cell proliferation

Recent studies have demonstrated an active role for neurons in glioma progression. Specifically, peritumoral neurons establish functional excitatory synapses with glioma cells, and optogenetic stimulation of cortical pyramidal neurons drives tumor progression. However, the specific role of different subsets of cortical neurons, such as GABAergic interneurons, remains unexplored. Here, we directly compared the effects of optogenetic stimulation of pyramidal cells vs. fast-spiking, GABAergic neurons. In mice inoculated with GL261 cells into the motor cortex, we show that optogenetic stimulation of pyramidal neurons enhances glioma cell proliferation. In contrast, optogenetic stimulation of fast-spiking, parvalbumin-positive interneurons reduces proliferation as measured by BrdU incorporation and Ki67 immunolabelling. Since both principal cells and fast-spiking interneurons are directly activated by sensory afferent input, we next placed tumors in the occipital cortex to test the impact of visual stimulation/deprivation. We report that total lack of visual input via dark rearing enhances the density of proliferating glioma cells, while daily visual stimulation by gratings of different spatial frequencies and contrast reduces tumor growth. The effects of sensory input are region-specific, as visual deprivation has no significant effect on tumor proliferation in mice with gliomas in the motor cortex. We also report that sensory stimulation combined with temozolomide administration delays the loss of visual responses in peritumoral neurons. Altogether, these data demonstrate complex effects of different neuronal subtypes in the control of glioma proliferation.

Spatial contrast sensitivity in patients with primary open-angle glaucoma and ocular hypertension

To study the characteristics of SCS in patients with POAG, PEG (as well as in the paired eye without glaucoma) and OH. The work was performed in the period from 2011 to July 2017. Analytical, observational case-control study data was analyzed. The study included 1380 patients under dynamic observation; in accordance with inclusion and non-inclusion criteria, 290 patients (540 eyes) with POAG, PEG, OH, as well as healthy people were included in the study. SCS was measured using 'Zebra v 3.0' software developed by the laboratory of clinical physiology of vision named after S.V. Kravkova in collaboration with 'Astroinform SPE' LLC. Patients were shown vertical achromatic (black and white) and colored (red, green, and blue) gratings of specific spatial frequencies (0.5; 1; 2; 4; 8; 16 cycles/degree). Among the patients of the study, 243 (83%) were female and 47 (17%) were male. The average age of all patients at the time of inclusion in the study was 67.75 (62.8; 74.5); 67.84±8.7 years. The study revealed an increase of SCS in patients with OH and their tendency for a slight increase in the contralateral eye with unilateral PEG in comparison with measurements taken from patients of POAG and PEG groups. The revealed increase of SCS is likely to be a consequence of increased or preserved hemodynamic characteristics in the vessels of the eye and orbit in patients with hypertension and in the contralateral eye in unilateral glaucoma, as described in our previous publications. At the same time, generalized changes in the vascular wall in patients with 'PEG-' on the paired eye only predetermine a tendency for an increase of SCS indices.

The north effect is more pronounced for orientation discrimination than simple detection of spatial frequency gratings.

The north effect is more pronounced for orientation discrimination than simple detection of spatial frequency gratings.

Unconscious processing of coarse visual information during anticipatory threat.

Rapid detection of threats has been proposed to rely on automatic processing of their coarse visual features. However, it remains unclear whether such a mechanism is restricted to detection of threat cues, or whether it reflects a broader sensitivity to even neutral coarse visual information features during states of threat. We used a backward masking task in which participants discriminated the orientation of subliminally presented low (3 cpd) and high (6 cpd) spatial frequency gratings, under threat (of shock) and safe conditions. Visual awareness of the gratings was assessed objectively using an additional localization task. When participants were unaware of the gratings, above chance and improved discrimination of low-spatial frequency gratings was observed under threat compared to safe trials. These findings demonstrate unconscious processing of neutral coarse visual information during threat state, supporting the view that automatic threat detection may rely on a general facilitation of coarse features irrespective of threat content.

Contrast Sensitivity in Eyes with Central Scotoma: Effect of Stimulus Drift.

In the field of visual rehabilitation of patients with central visual field loss (CFL), knowledge on how peripheral visual function can be improved is essential. This study presents measurements of peripheral dynamic contrast sensitivity (with optical correction) for off-axis viewing angles in subjects with CFL. Subjects with CFL rely on a peripheral preferred retinal locus (PRL) for many visual tasks. It is therefore important to ascertain that contrast sensitivity (CS) is maximized in the PRL. This study evaluates the effect of stimulus motion, in combination with optical correction, on CS in subjects with CFL. The off-axis refractive errors in the PRL of five young CFL subjects were measured with a COAS open-view Hartmann-Shack aberrometer. Low-contrast (25% and 10%) and high-contrast resolution acuity for stationary gratings was assessed with and without optical correction. High-contrast resolution was also measured for gratings drifting at 7.5 Hz (within a fixed Gaussian window). Furthermore, resolution CS was evaluated for both stationary and moving gratings with optical correction for a total of two to three spatial frequencies per subject. High-contrast resolution acuity was relatively insensitive to stimulus drift motion of 7.5 Hz, whereas CS for gratings of 0.5 cycles per degree improved with drift for all subjects. Furthermore, both high- and low-contrast static resolution improved with optical correction. Just as for healthy eyes, stimulus motion of 7.5 Hz enhances CS for gratings of low spatial frequency also in the PRL of eyes with CFL. Concurrently, high-contrast resolution is unaffected by the 7.5-Hz drift but improves with off-axis optical correction. This highlights the importance of providing optimal refractive correction for subjects with CFL and that stimulus motion can be used to further enhance CS at low spatial frequencies.

The time course of contrast sensitivity recovery after a pigment bleaching is delayed in subjects with abdominal obesity

PurposeThe abdominal obesity is an anthropometric marker associated with inflammation and age‐related macular degeneration (AMD). We examined the association between mesopic contrast recovery dynamics and abdominal obesity in older adults with normal macular health.Methods29 eyes of 29 healthy subjects (47–70 years) divided in two groups: a group without abdominal obesity (waist‐to‐height ratio (WHtR) &lt; 0.5; n = 15) and a group with abdominal obesity (WtHR ≥ 0.5; n = 14) were examined. The recovery of contrast sensitivity for sine‐wave gratings of low spatial frequency (1 cycles per degree) and low mean luminance (0.1 cd.m‐2) was measured within the central retina for 6 minutes in darkness after photo‐pigment bleaching. Sensitivity recovery functions were fitted to an exponential decay function. The time constant for recovery (tau, seconds), elevation and final contrast thresholds (CT) were calculated. The intersession repeatability of the method was determined by the Bland‐Altman coefficient of repeatability (COR). Visual acuity (VA), body mass index (BMI) and WtHR were obtained.ResultsThe mean tau was 42 s slower in the group with abdominal obesity (83.84 ± 35.78 s) than in the group without abdominal obesity (41.94 ± 13.70 s) (P &lt; 0.001). The mean elevation and final CTs did not vary significantly between groups. Forward stepwise regression analysis revealed that tau was independently correlated with WtHR (r = 0.74; P &lt; 0.0001), but not with BMI, CT, VA or age. There was no significant relationship between WtHR and CTs. Intersession repeatability of recovery measurements was high (tau, COR= ± 16 s).ConclusionsThe time constant for contrast sensitivity recovery after a pigment bleaching increases with abdominal obesity in eyes of older adults with normal macular health. Testing for the combination of these factors would allow for early detection of AMD.

The time course of contrast sensitivity recovery after a pigment bleaching is delayed in subjects with abdominal obesity

PurposeThe abdominal obesity is an anthropometric marker associated with inflammation and age‐related macular degeneration (AMD). We examined the association between mesopic contrast recovery dynamics and abdominal obesity in older adults with normal macular health.Methods29 eyes of 29 healthy subjects (47–70 years) divided in two groups: a group without abdominal obesity (waist‐to‐height ratio (WHtR) &lt;0.5; n = 15) and a group with abdominal obesity (WtHR ≥ 0.5; n = 14) were examined. The recovery of contrast sensitivity for sine‐wave gratings of low spatial frequency (1 cycles per degree) and low mean luminance (0.1 cd.m−2) was measured within the central retina for 6 minutes in darkness after photo‐pigment bleaching. Sensitivity recovery functions were fitted to an exponential decay function. The time constant for recovery (tau, seconds), elevation and final contrast thresholds (CT) were calculated. The intersession repeatability of the method was determined by the Bland‐Altman coefficient of repeatability (COR). Visual acuity (VA), body mass index (BMI) and WtHR were obtained.ResultsThe mean tau was 42 s slower in the group with abdominal obesity (83.84 ± 35.78 s) than in the group without abdominal obesity (41.94 ± 13.70 s) (p &lt; 0.001). The mean elevation and final CTs did not vary significantly between groups. Forward stepwise regression analysis revealed that tau was independently correlated with WtHR (r = 0.74; p &lt; 0.0001), but not with BMI, CT, VA or age. There was no significant relationship between WtHR and CTs. Intersession repeatability of recovery measurements was high (tau, COR = ±16 s).ConclusionsThe time constant for contrast sensitivity recovery after a pigment bleaching increases with abdominal obesity in eyes of older adults with normal macular health. Testing for the combination of these factors would allow for early detection of AMD.

Color weight photometry

We study the “color weight” for a number of rather different paradigms. In well researched heterochromatic photometry methods we find that the “weights” determined by settings of naive observers are closely determined by the CIE luminance functional. This is very different for tasks that involve mid- and high-level aspects of perception. In several cases we find equipollence for the display red, green and blue channels. Moreover, in such cases the very nonlinear maximum-rule fits the data rather better than a linear functional. These findings are of interest when photometry needs to be applied for stimuli that are different from the high temporal and low spatial frequency gratings typical for flicker photometry. These results are relevant for science, ergonomics and art.

The "Spinner" Illusion: More Dots, More Speed?

The perceived speed of a ring of equally spaced dots moving around a circular path appears faster as the number of dots increases (Ho & Anstis, 2013, Best Illusion of the Year contest). We measured this “spinner” effect with radial sinusoidal gratings, using a 2AFC procedure where participants selected the faster one between two briefly presented gratings of different spatial frequencies (SFs) rotating at various angular speeds. Compared with the reference stimulus with 4 c/rev (0.64 c/rad), participants consistently overestimated the angular speed for test stimuli of higher radial SFs but underestimated that for a test stimulus of lower radial SFs. The spinner effect increased in magnitude but saturated rapidly as the test radial SF increased. Similar effects were observed with translating linear sinusoidal gratings of different SFs. Our results support the idea that human speed perception is biased by temporal frequency, which physically goes up as SF increases when the speed is held constant. Hence, the more dots or lines, the greater the perceived speed when they are moving coherently in a defined area.